Conventionally, a developing cartridge includes a detection protrusion for moving an actuator positioned at a main body casing of an image forming apparatus. The detection protrusion has a gear. The detection protrusion is rotatable around a shaft. The actuator is moved by the detection protrusion pushing the actuator during rotation of the gear. Further, the gear has a toothless portion. In a case where the toothless portion faces a drive gear that transmits the drive force to the gear, meshing between the gear and the drive gear is released. As a result, the rotation of the gear stops. As the rotation of the gear stops, the rotation of the detection protrusion also stops.